[PATCH] powerpc/mm: Use jump label to speed up radix_enabled check

Aneesh Kumar K.V aneesh.kumar at linux.vnet.ibm.com
Wed Apr 27 17:00:30 AEST 2016


Benjamin Herrenschmidt <benh at kernel.crashing.org> writes:

> On Wed, 2016-04-27 at 11:00 +1000, Balbir Singh wrote:
>> Just basic testing across CPUs with various mm features 
>> enabled/disabled. Just for sanity
>
> I still don't think it's worth scattering the change. Either the jump
> label works or it doesn't ... The only problem is make sure we identify
> all the pre-boot ones but that's about it.
>

There are two ways to do this. One is to follow the approach listed
below done by Kevin, which is to do the jump_label_init early during boot and
switch both cpu and mmu feature check to plain jump label.

http://mid.gmane.org/1440415228-8006-1-git-send-email-haokexin@gmail.com

I already found one use case of cpu_has_feature before that
jump_label_init. In this approach we need to carefully audit all the
cpu/mmu_has_feature calls to make sure they don't get called before
jump_label_init. A missed conversion mean we miss a cpu/mmu feature
check.


Other option is to follow the patch I posted above, with the simple
change of renaming mmu_feature_enabled to mmu_has_feature. So we can
use it in early boot without really worrying about when we init jump
label.

What do you suggest we follow ?

-aneesh



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